The present invention concens a summer cap made of open-meshed fabric of polyester yarn. There have been developed many varieties of the cap; one of which is the summer cap having a large visor to shield the summer daylight or made of open-meshed fabric to make ventilation. However, such summer cap has no positive means to effectively cool the head of a person working in the field, so that the worker must suffer the heat of the sun or other high temperature environment (e.g. steel mill) or where the user generates heat by exertion, e.g. exercise, manual labor.